1. Field of the Invention
The present invention relates to a vehicle headlight optical axis direction adjusting system for automatically adjusting the optical axis direction of irradiation of a headlight provided for a vehicle.
2. Description of Related Art
Conventionally, in the headlight of a vehicle, when the optical axis of the a headlight is directed upward due to inclination of the chassis of the vehicle, glare is given to an on-coming vehicle or the like. When the optical axis is directed downward, a driver of the vehicle may lose the far field of view. There has been, consequently, a demand for holding the optical axis direction of the headlight unchanges as much as possible.
JP-A-9-301055 discloses a vehicle headlight optical axis control system, in which a control mode is set in accordance with acceleration, a filtering process is executed when the acceleration is smaller than a predetermined value, the filtering process is not performed so as not to delay switching of the control mode when the acceleration is equal to or larger than the predetermined value, and the optical axis direction of the headlight is adjusted on the basis of a change in the height of the vehicle on each occasion.
In the above system, when the acceleration of the level which can not be reached in a normal driving state is sensed in association with a known traction (TRC) control or antilock brake (ABS) control, since the acceleration is equal to or larger than the predetermined value, the filtering process is not performed and the control mode is frequently switched. At the time of acceleration associated with the TRC control (TRC control time) or at the time of deceleration associated with the ABS control (ABS control time), although the acceleration largely changes, the vehicle posture does not change so much. As a result, the optical axis is improperly controlled when the direction of the optical axis of the headlight is allowed to follow changes in the acceleration at such time.
Another optical axis control system is known which uses an inclination angle obtained by approximating an amount of change in the vehicle posture caused by loading to a linear expression. According to this control, the optical axis direction of the headlight can be made to coincide with the vehicle posture under a limited loading condition such as "only occupant load" or "occupant load and up to 50 kg of trunk load". However, various loading conditions of combination of the occupant load and the trunk load can not be dealt with.
In a still another system, a vehicle height sensor is installed only on either the right or left side of a rear wheel since front wheels are wheels to be steered and an installation space is limited. A front height value is estimated on the basis of a rear height value in the stop mode of the vehicle to calculate the inclination angle. When the vehicle is stopped riding on a block or the like, a rear height value different from that on a flat road is sensed. In one trip (a driving interval between stops of the vehicle) after that, there is consequently an inconvenience such that a computation error occurs in the inclination angle in the longitudinal direction of the vehicle and the optical axis direction of the headlight is deviated. Since the rear height value changes due to turning which is a rotary motion around the longitudinal axis of the vehicle during a turn although the vehicle is not inclined in the longitudinal direction, a computation error occurs in the inclination angle in the longitudinal direction of the vehicle until the turn of the vehicle is finished and there is an inconvenience such that the optical axis direction of the headlight is accordingly deviated.